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Custom Types

Serialization

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  • Overview
  • Custom Classes
  • Serializing Custom Classes
  • Deserializing Custom Classes

Overview

In this guide, you can learn how to use PyMongo to serialize your custom types.

Serialization is the process of mapping a Python object to a BSON document for storage in MongoDB. PyMongo automatically converts basic Python types into BSON when you insert a document into a collection. Similarly, when you retrieve a document from a collection, PyMongo automatically converts the returned BSON back into the corresponding Python types.

For a complete list of Python-to-BSON mappings, see the bson API documentation.

Custom Classes

To serialize and deserialize custom Python classes, you must implement custom logic to handle the conversion. The following sections show how to serialize and deserialize custom classes.

Serializing Custom Classes

To serialize a custom class, you must convert the class to a dictionary. The following example serializes a custom class by using the vars() method, and then inserts the serialized object into a collection:

class Restaurant:
    def __init__(self, name, cuisine):
        self.name = name
        self.cuisine = cuisine
restaurant = Restaurant("Example Cafe", "Coffee")
restaurant_dict = vars(restaurant)
collection.insert_one(restaurant_dict)

The preceding example serializes the Restaurant object into the following dictionary:

{'name': 'Example Cafe', 'cuisine': 'Coffee'}

To learn more about inserting documents into a collection, see the Insert Documents guide.

Deserializing Custom Classes

To deserialize a custom class, you must convert the dictionary back into an instance of the class. The following example retrieves a document from a collection, and then converts it back into a Restaurant object from the preceding example:

def deserialize_restaurant(doc):
    return Restaurant(name=doc["name"], cuisine=doc["cuisine"])
restaurant_doc = collection.find_one({"name": "Example Cafe"})
restaurant = deserialize_restaurant(restaurant_doc)

To learn more about retrieving documents from a collection, see the Find Documents guide.

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